In the field of storage systems using hard magnetic disks, also known as Winchester drives, the speed at which data is read from and written to the disks is an important measure of performance. A hard disk drive that reads and writes data quickly complements a fast computer. However, a hard disk drive that reads and writes data slowly detracts from the performance of an otherwise fast computer. Thus, as computers are designed to operate at ever-higher speeds, components which do not operate rapidly, or which have high operating power requirements are stumbling blocks which are encountered.
One such component is the head positioner that carries the magnetic heads to the appropriate tracks on the disks. The rotary moment of inertia of the positioner arms forming part of the head positioner is a critical factor in determining the speed at which the heads can be positioned to read data from the storage disks. Solid head positioner arms have been widely used for their rigidity, but have the disadvantage of a relatively high moment of inertia. It has also been proposed to use open arm constructions to reduce the moment of inertia. As the rotary moment of inertia is reduced, the arm offers less resistance to rotary motion and therefore can be positioned more rapidly and with less power. However, certain prior art positioners, including rotary positioners, have relatively long and flexible arms. Such elongated head positioner arms tend to have modes of vibration which are easily excited during normal operation of the disc drive. Hence, as the positioning speed increases, the arms are more prone to bending, twisting and vibration, which put the magnetic heads out of alignment with the data tracks and adversely affect the time required for the heads to settle after a "seek", changing from one track to another.
U.S. Pat. No. 4,843,503 discloses one attempt to provide reduced inertia arms, and also includes a damping device formed of a compressible visco-elastic material which is inserted between at least two adjacent head arms to reduce the uncontrolled vibratory motion, apparently due to the open configuration of the arms. The added damping device adds more rotary inertia to the arms, thereby increasing the power required to rotate the arms a certain distance in a given time.
In addition to the problem with uncontrolled vibration, previous attempts to reduce the rotary inertia of head positioning arms have failed for other reasons. U.S. Pat. No. 4,805,055 discloses an arm provided with four triangular-shaped holes which reduce the weight and rotary inertia. A serious drawback of this design is that counterweights must be used to balance the arm, thereby adding back at least some portion of the inertia that the holes are intended to reduce. Another approach is taken in U.S. Pat. No. 4,716,478, which discloses an arm provided with three triangular-shaped holes, each with a vertex pointed at the vertex of another triangle. Unfortunately, the arm profile is excessively wide and assymetrical, causing the rotary inertia to be greater than necessary.
Accordingly, a principal object of the present invention is to provide an improved head positioner arm with which the magnetic heads can be positioned with greater speed and less power, and without significant bending, twisting, vibration and the like.